1. Field of the Invention
The present invention relates to a method for improving the manufacture of disk drives. More specifically, the invention involves the determination of a spindle rotation speed for writing servo tracks to a disk drive based on measured servo performance of a head-disk assembly.
2. Description of the Related Art
Disk drives are principal components in the vast majority of computer systems. The drives store information in a non-volatile manner and can be readily written, read, and re-written. Large amounts of information can be stored on disk drives reliably at low cost.
A typical disk drive consists of one or more rigid disks or xe2x80x9cplattersxe2x80x9d that are attached to a spindle. The spindle is attached to a spindle motor which rotates the spindle and the attached platter or platters. The surfaces of the platters comprise a magnetic medium. As the platters rotate, magnetic heads write magnetic transitions to or read magnetic transitions from the medium.
The magnetic storage portion of the disk platters is organized into substantially concentric circular regions. Each circular region is divided into arcuate sectors formed by regular angular wedge-like demarcations around the disk. The magnetic read and write heads are attached to an actuator that moves the head to read or write a particular sector of the platter or platters. Positioning of the read or write head is achieved via the use of servo tracks that are written to the disk. The servo tracks are written at intervals around the disk and on each side of a region of the disk that is to contain data. The position of the head on the disk is determined by reading the servo tracks, and consequently, the servo tracks must be accurately placed on the drive medium.
For the disk to be used, servo tracks must be placed on the disk. The tracks can be etched or printed onto the disk medium, written by a servo track writer, or self-written by the disk drive. Additionally, the servo tracks can be written by a combination of these servo track writing techniques.
The placement of servo tracks onto the disk of a disk drive is an important part, but a potentially time consuming part, of the manufacture of disk drives. Although etching or printing of the servo tracks onto the disks can produce a high volume of disks containing servo tracks very quickly, these methods can not produce the density of servo tracks on a disk that is needed for modem high capacity hard drives. Dedicated servo track writers can produce the density of servo tracks needed for modem drives, but the specialty manufacturing equipment is expensive, and the number of servo track writers used during the manufacturing process is typically limited. Self-writing of all or a portion of servo tracks by the disk drive itself does not require special manufacturing equipment, but is the slowest way to place the servo tracks onto a disk.
A first aspect of the present invention is a method for determining a spindle rotation speed to be used for writing servo tracks on a head-disk assembly which will be incorporated into a fully assembled disk drive. The head-disk assembly comprises a recording head, a rotary actuator, a spindle motor, and a storage medium. The storage medium is coupled to the spindle motor and has an inner circumference and outer circumference with a magnetic storage portion between the inner and outer circumference.
The position error values of at least one servo track are measured. A position error metric is generated by analyzing the position error values. A spindle speed for writing servo tracks is selected based upon the value of the position error metric.
Another aspect of the present invention is a servo track writer that writes calibration tracks on the storage medium of a head-disk assembly, and that determines the operational disk spindle rotation rate. The servo track writer comprises a controller, a servo performance measurement circuit, and a servo track writer speed selector. The controller processes a clock reference pattern to determine the location of the write element and directs the head to write the servo tracks on the storage medium. The servo performance measurement circuit measures position error values of the servo tracks written on the head-disk assembly and generates a position error metric value. The servo track writer speed selector calculates a desired servo track writer speed from the value of the position error metric generated by the servo performance measurement circuit.